matplotlib is a python 2D plotting library which produces publication quality
figures using in a variety of hardcopy formats (PNG, JPG, PS, SVG) and
interactive GUI environments (WX, GTK, Tkinter) across platforms. matplotlib
can be used in python scripts, interactively from the python shell (ala matlab
or mathematica), in web application servers generating dynamic charts, or
embedded in GTK, Tk or WX applications; see backends.

WWW: http://matplotlib.sourceforge.net/